In FIG. 1, a permanent magnet motor includes a stator 100 in the form of an annular ring and a rotor 102 rotatably accommodated in a hollow part 101 formed at the central area of the stator 100. In the stator 100, there are formed, at regular intervals, a plurality of teeth 103 projecting toward the inner circumferential side of the stator and a plurality of slots 104 each positioned between two adjacent teeth 103. Wound around each of the teeth 103 is a conductive wire 105 that is wired in the slots 104 on both sides of each tooth.
Winding of the conductive wires 105 around the teeth 103 is accomplished by using a bobbin machine having a plurality of nozzles arranged in a radial manner. For instance, when winding the conductive wires around six teeth 103 with the use of a bobbin machine with three nozzles, the winding is accomplished by two processes: a first winding process of winding a conductive wire around three teeth 103 arranged alternately; and a second winding process of winding a conductive wire around the other three teeth 103.
In this winding process, the bobbin machine is driven so that the nozzles go around the teeth 103 to be wound, and the conductive wires 105 getting out of the nozzles are wound around the teeth 103. For this reason, between the adjacent conductive wires 105 wound around the adjacent teeth 103, a gap 106 is defined in order to allow the nozzle to go around each of the teeth 103. This gap 106 is formed to be larger than the outer diameter of the nozzle.
In this way, since the gap 106 is formed between the conductive wires 105 wound around the adjacent teeth 103 and furthermore, the gap 106 is formed to be larger than the outer diameter of the nozzle, it is necessary to increase a cross-sectional area of the slot 104 (i.e. cross-sectional area in a plane perpendicular to the rotating axis of the rotor 102) by the gap 106 in addition to the cross-sectional area of the wound conductive wire 105.
If the cross-sectional area of each slot 104 increases, then the magnetic path about each of the teeth 103 and its continuous core portion of the stator 100 is narrowed that much to increase the density of flux with increased excitation loss, causing a problem of reducing the efficiency of the permanent magnet motor.
In order to solve such a problem, Japanese Patent Publication Laid-open No. 2004-274878 discloses one invention where a gap between the conductive wires wound around the adjacent teeth is reduced to decrease the cross-sectional area of each slot, so that the magnetic-path width can be increased to improve the efficiency of an electrical motor.
In this invention, using a bobbin machine equipped with the same number of nozzles as the number of slots, the winding operation is performed against all of the teeth simultaneously. Then, at a time of winding the conductive wire in the outermost circumference, the nozzles are moved from the interior side of the slots toward the inner circumferential side of the stator, making a gap between the adjacent conductive wires smaller than the outer diameter of the nozzle.